This invention is related to an electrical power source. More specifically, this invention is related to a metal inert gas (MIG) brazing power source with unique transformer and inductor designs.
Zinc coated steel has been used extensively in welding because of their resistance to corrosion damage. However, joining galvanized sheet steels faces a basic problem in that they produce zinc vapor when heated at high temperatures. Zinc starts to melt at a temperature around 420xc2x0 C. and vaporize at around 907xc2x0 C. These properties have an unfavorable effect on the arc welding operation because as soon as the electric arc is generated, zinc vapors are formed, causing arc instability, and leading to other problems such as porosity and excessive spattering. The heat generated by the high temperatures causes burn-through and destruction of the zinc coating, thus decreasing the corrosion resistance. Because of these problems, it is necessary to reduce the heat generated in the arc column during the welding of galvanized steel sheets. In order to obtain such results, it is necessary not only to combine appropriate wires and shielding gases, but also to use welding power sources with very particular characteristics.
The problems caused by heat have limited the use of Gas Metal Arc Welding (GMAW) process to join these materials and determining the adoption of MIG brazing as an alternative joining process to be used for galvanized sheet steels.
In terms of equipment, MIG brazing appears to be similar to GMAW, although it is based on a totally different concept. While GMAW aims to produce a welded joint composed by the fusion of base and filler metals, MIG brazing joins the materials by wetting and capillary action, without melting the base material. The use of lower melting point filler metal, as in MIG brazing, requires lower heat input, and consequently, reduces the zinc coating damage. However, to achieve this benefit, optimized metal transfer conditions have to be selected in order to avoid spattering and coating burn-off. The equipment characteristics have an important role to play in controlling metal transfer. Consequently, the power source to perform MIG brazing has different requirements regarding heat distribution and arc characteristics. Then, it would be expected that MIG brazing power sources were customized to this operation, instead of using the same equipment used for GMAW.
There exists some electronic equipment having characteristics required by MIG brazing of plate thickness higher than 0.8 mm. Nevertheless, they are very complex to control process parameters, very expensive and of high maintenance cost. On the other hand, the existing electromagnetic equipment does not have suitable output characteristics for MIG brazing operation. These restrictions have limited the use of MIG brazing of galvanized steel to less complex applications and for few materials/coating thickness. At present, there are three commercial available options for MIG brazing equipment. The first one uses the same electromagnetic power source as conventional GMAW that is unsuitable, as described above. The second and third options rely on very sophisticated electronic power sources, pulsed or not, which are much more expensive and hard to select optimized parameters set. The pulsed power sources have an additional difficulty in that the zinc layers are greater than 20 mm and the plate thickness are lower than 0.8 mm. Even with these limitations, the current application for MIG brazing to join galvanized steel sheet is predominantly with the electronic power sources, using pulsed arc. This option is suitable for automatic processes, which can justify high investment in this kind of power sources and can operate at high travel speeds that are demanded by pulsed spray arc brazing of thin plates. However, the use of electronic power sources, especially in a pulsed arc mode, has not satisfied the demands for MIG brazing of galvanized sheet steels.
The high cost of electronic equipment and their difficulty in joining thinner plates and/or thicker coating layers have led many users to try use the electromagnetic power sources as an option to perform MIG brazing.
U.S. Pat. No. 5,611,950 discloses some design changes in an electromagnetic welding power source in order to supply a stable welding current having a smooth waveform and enough short circuit current. The approach used in this patent includes the connection in parallel of extra rectifiers and capacitors with the rectifying circuit in order to minimize the ripple of the current and voltage waveforms. This approach, besides substantially increasing the manufacturing cost, does not provide the desirable results in terms of arc stability and outputs characteristics that are reqired by the MIG brazing process.
It is therefore an objective of this invention to develop a conventional dedicated power source for MIG brazing, especially for galvanized sheet steels, but not limited to these materials, with the individual advantages of electronic power sources, i.e., good arc stability and low spattering level, and of electromagnetic power sources, i.e., easy parameters adjustment and low investments and maintenance costs.
It is another objective of this invention to develop a conventional dedicated power source for MIG brazing with no limitations regarding minimum plate thickness and also regarding maximum coating layer thickness as observed in electronic pulsed and existing electromagnetic power sources.
It is an additional objective of the invention to develop a conventional dedicated power source to be used in MIG brazing that is less expensive, easier to control process parameters, with lower maintenance cost and allowing excellent brazed joint quality.
One aspect of this invention is directed to a power source for MIG brazing that comprises a concentric type transformer having a specific magnetic core and certain coils having specific characteristics, as well as an inductor having a magnetic core with specific characteristics and certain coils having specific characteristics.
Another aspect of this invention is directed to a power source for MIG brazing that comprises a concentric type transformer that has a specific magnetic core and specific coils.
Yet another aspect of this invention is directed to a power source for MIG brazing that comprises an inductor that has a specific magnetic core and specific coils.